A conventional motor control device rotationally drives a rotor of a motor to a target rotation position by switching over current supply phases of the motor based on output signals of an encoder. JP 2008-32176 A (US 2008/0024081 A1) discloses a motor control device, which rotationally drives a motor of a shift-by-wire system of an automatic transmission of a vehicle. This motor control device limits power supply to the motor when a heat generation state is detected, so that the shift-by-wire system is protected from failure, which is caused by heat generation of the motor control device. The heat generation is caused when the current supply phases are switched over.
In the motor control device described above, convenience is low because power supply to the motor is lowered when the heat generation state is determined. That is, in the heat generation state, the motor does not rotate and the motor is not controlled to rotate even when a driver manipulates a shift lever of the automatic transmission.